737 MAX, the engine swap that become a nightmare

The Boeing 737 is the plain vanilla single aisle airliner that flies most airline routes, the ordinary routes that don't, will never, generate enough traffic to fill up a bigger plane.  It's been in production for decades.  Under competitive pressure from Airbus, Boeing decided to do an engine swap on the trusty long serving 737.   Metallurgists have come up with better hot section metals over the years, the better metals allow the engine to run hotter, which gives better fuel mileage, as much as 10% better.   And, Boeing and the FAA promised that the re-engined 737 would fly just like the good old 737 and not require retraining pilots to fly the new aircraft.
   The new engines are good, and do deliver better fuel economy.  They are also bigger, so much bigger that they almost drag  on the runway.  Which means the new engines mount lower beneath the wings.  Which means you get a stronger nose up motion when the throttles are advanced.  Boeing, with FAA approval, decided to modify the autopilot to apply some nose down force using the trim tabs to make the 737 MAX fly like the good old 737.   And something went wrong, and two brand new 737 MAXs dove into the ground right after takeoff, killing all on board.   Aviation Week hasn't told us just what went wrong, but two smoking holes in the ground are enough to convince most of us that something is wrong.